There is known a conventional board mounted electrical connector, as disclosed in Japanese Unexamined Patent Publication No. 9(1997)-069371. This connector comprises contacts, which are arranged in three rows, and an insulative housing, for holding the contacts. Each of the contacts of this connector comprises a contact portion, which has an axis substantially parallel to a circuit board, on which the housing is mounted; and a leg portion, which extends outwardly from the rear wall of the housing, then extends in a direction perpendicular to the axis of the contact portion, and is received in apertures of the circuit board. Each leg portion comprises an extending portion that extends away from the circuit board from the rear wall of the housing; a flexible portion, which is formed continuously with the extending portion; and a linear portion that extends substantially perpendicular to the circuit board from the flexible portion.
In board mounted electrical connectors, rates of thermal expansion differ between insulative housings that form the connectors, and circuit boards that the insulative housings are mounted on. Due to the difference in the rates of thermal expansion, degrees of expansion and contraction of parts due to changes in temperature differ. As a result, stress is generated at connecting portions (soldered portions) between contacts and the circuit board, which may cause the soldered portions to crack. For this reason, the known electrical connector has adopted the extending portions that extend away from the circuit board, thereby extending the entire lengths of the leg portions. The extended lengths of the leg portions absorbs dimensional differences due to expansion and contraction of parts, in an attempt to reduce the stress applied on the connecting portions between the contacts and the circuit board. As a result, the dimensions of the leg portions are enabled to be made larger, even if spacing between the contacts and the circuit board are small. Accordingly, low profile, high density mounting of connectors on circuit boards is capable of being realized.
Normally, the leg portions of contacts are plated with solder that contains lead. This is because the leg portions are soldered to the circuit board with solder that contains lead, and if the leg portions are plated with solder that contains lead, the connection properties are favorable. As a result, there is a possibility that the lead will pollute the environment during production of the electrical connector, or upon disposal of the connector. In the case that the entirety of the leg portions is plated with a metal such as tin that does not contain lead (lead free solder), the possibility of environmental pollution is decreased. However, whiskers (phenomena in which needle like crystals are generated on the surface of the plating) may be generated at the flexible portions of the leg portions. The cause of these whiskers is internal stress, which is generated in the contacts, and the whiskers are likely to appear at the flexible portions. If whiskers are generated, they cause adjacent contacts to short, thereby causing a problem that desired electrical connection properties cannot be obtained.